Multi-directional seismic exploration methods

ABSTRACT

A number of seismic detectors are located in a two-dimensional array on the surface of the earth, either on land or at sea. One or more seismic disturbances are produced in the vicinity of the seismic detectors at points located to produce sampling of various subsurface reflection points to form one or more twodimensional areas of coverage. For each seismic disturbance, the subsurface reflections thereof received by the various seismic detectors are recorded. In some embodiments, the seismic disturbances are produced at points located to produce multidirectional sampling of each of various subsurface reflection points and recordings for different ones of the seismic disturbances are combined to produce stacked recordings wherein multi-directional reflections from common subsurface points are added.

Waited States Patent Davis July 17, 1973 MULTl-DIRECTIONAL SEISMIC Primary ExaminerBenjamin A. Borchelt EXPLORATION METHODS Assistant lixaminerJ. V. Doramius [75] Inventor: Jlee Davis, Dallas Tex Attorney-(nles Cv Llegg, Jr., Calvin E. lhorpe and Richard E. Bee

[73] Assignee: Avance Oil and Gas (10., Inc.,

Midland, Tex.

[57] ABSTRACT [22} Filed: May 21,1971

Appl. No.: 145,811

A number of seismic detectors are located in a twodimensional array on the surface of the earth, either on land or at sea. One or more seismic disturbances are produced in the vicinity of the seismic detectors at points located to produce sampling of various subsurface reflection points to form one or more twodimensional areas of coverage. For each seismic disturbance, the subsurface reflections thereof received by the various seismic detectors are recorded. In some embodiments, the seismic disturbances are produced at points located to produce multi-directional sampling of each of various subsurface reflection points and re cordings for different ones of the seismic disturbances are combined to produce stackedl recordings wherein multi-directional reflections from common subsurface points are added.

21 Claims, 4 Drawing Figures Patented July 17, 1973 4 Sheets-Sheet 1 FIG.

Patented July 17, 1973 4 Sheets-Sheet 2 ['IITIIIIIIIIIIIIIIIIIIIIIIII IIlllllllllll III'IIIII ID ID IO N S l XV A 51 SOURCE IIIIIII'IIIIIIIIIIIIIIITI IIIIIIIII1II'IIIYIIII! SUBSURFACE REFLECTION POINT X AXIS Patented July 17, 1973 3,746,122

4 Sheets-Sheet 5 0 O 0 S O 0 O O 0 (e) (s) (e) (4) (4) (4) (z) (2) (2) Patented July 17, 1973 4 Sheets-Sheet 4 mokuwkwo momnow IIIIIIIIIIIIIIIllllllll l l IIIIIIIIIIIIIIIIIIIIIIII IO N SIXVY A MULTI-DIRECTIONAL SEISMIC EXPLORATION METHODS BACKGROUND OF THE INVENTION This invention relates to seismic exploration methods for determining the location and course of subsurface earth structures.

A common method of seismic exploration is carried out by locating a string of spaced seismic detectors along a straight line at the surface of the earth. A seismic source is located in line with the detectors and operated to produce a seismic distrubance. Such disturbance produces subsurface reflections which are received by the detectors and recorded for later analysis. The string of detectors is then picked up and relocated either along a second line running parallel to the first line or at a new location in line with the first line and the foregoing process repeated for the second location. This process is continued until the desired area has been surveyed. As is apparent, this process can become rather tedious and time consuming where a relatively large surface area of the earth is to be surveyed.

A known problem which exists in the seismic exploration art is that of distinguishing the desired subsur face earth structure reflection signals from various extraneous seismic vibrations which are also received by the detectors and which are commonly referred to as noise. A known technique for minimizing such noise is commonly referred to as stacking. Such stacking technique involves the use of multiple sources for obtaining multiple reflections from a common subsurface point. After appropriate processing, the individual rec cordings for' the common subsurface point are combined to produce a composite record wherein the desired signal components are emphasized and the undesired noise components are minimized. This stacking technique is described in greater detail in U. S. Pat. No. 2,732,906, granted to W. H. Mayne on Jan. 31, 1956, and in U. S. Pat. No. 3,040,833, granted to H. L. Mendenhall and S. D. Elliott on June 26, 1962.

It is an object of the present invention to provide new and improved methods of seismic exploration for obtaining a greater amount of data concerning subsurface earth structures for a given expenditure of time and labor or conversely, for obtaining a given amount of data for a lesser expenditure of time and labor.

It is another object of the invention to provide new and improved seismic exploration methods for enabling a greater degree of stacking for a given expenditure of time and labor.

It is a further object of the invention to provide new and improved seismic exploration methods for obtaining better data concerning subsurface earth structures.

For a better understanding of the present invention, together with other and further objects and features thereof, reference is had to the following description taken in connection with the accompanying drawings, the scope of the invention being pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS Referring to the drawings:

FIG. 1 is a perspective view of a volume of the earth and showing in a simplified manner one of the basic concepts of the present invention;

FIG. 2 is a plan view showing a two-dimensional layout of seismic sources and detectors on the surface of the earth in accordance with an areal embodiment of the invention;

FIG. 3 is a plan view of a seismic source and detector layout in accordance with a lineal embodiment of the invention; and

FIG. 4 is a plan view of an area of the earth's surface and showing a further layout of seismic sources and detectors in accordance with a further embodiment of the invention.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS FIG. 1 shows a three-dimensional volume of earth structure 10, the surface of the earth being indicated at 11 and the upper surface of a subsurface earth strata being indicated at 12. In accordance with one embodiment of the invention, seismic sources 8,8 etc. and seismic detectors D D etc. are located in a twodimensional array at the earths surface 11 for obtaining a multi-directional sampling of each of various subsurface reflection points, one of such points being indicated at R in FIG. 1. Reflection pointR is located on the subsurface boundary plane 12. Seismic sources S,S etc. are fired in a sequential manner to produce a time spaced series of seismic disturbances. For the subsurface point R, the seismic disturbance produced by source S produces a seismic energy ray path 13 such that the relfection from the point R is received by the seismic detector D Similarly, a portion of the energy produced by the seismic disturbance produced by source S follows ray path 14 and is received by seismic detector D The seismic disturbances received by each ofthe various detectors D D etc. are recorded by the usual type of signal recording apparatus (not shown), such apparatus being connected to the various detectors by means appropriate signal conducting cables (not shown).

For each of the source-detector pairs shown in the idealized case of FIG. 1, the angle of incidence of the ray path is equal to the angle of reflection and the subsurface point R is located midway between the particular source and detector being considered. Additional source-detector pairs may be located on the circle 15 to produce additional samplings of the subsurface reflection point R along additional lines running in various additional compass directions. Similarly, further source-detector pairs can be located onopposite sides of additional circles, such as the circle 16, which are concentric with the circle 15. In this manner, there can be developed a solid cone of data regarding the subsurface reflection point R. One practical consequence of this is that during the subsequent analysis the various pieces of data can be examined and only those pieces which give the best results can be: selected and used to provide the final analysis. Also, as will be seen shortly, the basic concept of FIG. I can be readily extended to obtain multi-directional sampling of a relatively large number of subsurface reflection points during one and the same operation.

Referring to FIG. 2, there is shown a plan view of a selected area on the surface of the earth. For accuracy of explanation, an imaginary X and Y coordinate system has been superimposed on the plan view of FIG. I, the X axis scale of units being indicated at 17 and the Y axis scale of units being indicated at 18. For sake of example only, each distance unit on the X and Y scales may correspond to a physical distance of feet, in

which case the overall seismic array shown in FIG. 2 would cover an area of better than 1 square rnile.

The seismic exploration system of FIG. 2 is an example of the manner in which the multi-directional sampling technique of FIG. 1 can be applied to a relatively large number of subsurface reflection points for purposes of providing a two-dimensional coverage of a relatively large area.

The seismic array of FIG. 2 includes a relatively large number of seismic sources S and a relatively large number of seismic detectors D located in a two-dimensional array covering a substantial surface area of the earth. Each of the sources S is represented by a small square with a dot in the center thereof, while each of the detectors D is represented by a small circle with a dot in the center thereof. The various subsurface reflection points R which are sampled are represented by small dots. As thus seen, the FIG. 2 array includes four parallel lines along which are disposed both sources S and detectors D, these lines being located at Y 0, Y 16, Y 32, and Y 48 and extending parallel to the X axis. The FIG. 2 array also includes four additional lines along which only detectors D are disposed, these lines being located at Y 8, Y 24, Y 40 and Y 56 and extending parallel to the X axis.

In addition to being parallel, the various sourcedetector and detector only lines are spaced a substantial distance apart. As used in this specification and the appended claims, the term substantial distance denotes a distance of 100 feet or more. Preferably, the spacing between detector lines is greater than the spacing between neighboring detectors on the same line. In the illustrated embodiment, neighboring detectors on the same line are spaced four units apart, while adjacent detector lines are spaced 8 unitsapart. Neighboring sources S on the same line are spaced 12 units apart and are located at points which are different from the detector D locations.

The seismic sources S may be of the impulses type or of the vibratory type. The seismic detectors D may take the form of various ones of the different types of seismometers and geophones which are known in the seismic art. Also, it is to be understood tht each detector D, while spoken of in the singular, may, in fact, comprise a number of detectors grouped together in a cluster surrounding the common detector point for purposes of discriminating against undesired horizontally propagated seismic energy, this technique being known in the seismic art.

The detectors D in the lower four lines are connected to multiconductor cables which are, in turn, connected to appropriate signal recording apparatus in a recording truck 21. Similarly, the detectors D in the upper four lines are connected to multiconductor cables 22 which are, in turn, connected to signal record ing apparatus in a second recording truck 23. In both cases, the recording apparatus is preferably of the magnetic tape recording type.

Each of the 20 seismic sources S in FIG. 2 is caused to produce a seismic disturbance at a time which is different from the times at which the other sources 8 produce their disturbances. For each seismic disturbance, the resulting subsurface reflection signals which are produced by the 96 seismic detectors D are individually recorded on separate tracks on magnetic tape in the trucks 21 and 23. These field tapes are subsequently played back or reproduced in a coordinated manner for providing improved indications of the subsurface geology. This can be done in several different ways to accomplish several different purposes.

A particularly important purpose which can be accomplished with the FIG. 2 array is the stacking of reflections from common subsurface points continued for purposes of producing seismic records wherein the effect of seismic noise is minimized The manner of combining the individual recordings or traces obtained for a given subsurface reflection point is pretty much the same as that employed in connection with the known stacking technique. Briefly, the individual field recordings for the given point are played back and processed in such a manner as to apply the customary elevation, weathering and normal moveout corrections thereto, the corrected traces being individually recorded on a second magnetic tape. The second tape is then played back and the individual corrected signals are combined to produce a single composite signal which is then recorded to provide a composite record wherein the reflections from the common subsurface point augment one another. At the same time, the undesired noise vibrations, which are of a more or less random character for the different directions, more or less cancel one another so as to minimize the net noise component in the final composite record. One form of magnetic recording apparatus suitable in a general sense for accomplishing this stacking process is described in the above-mentioned U. S. Pat. No. 3,040,833 to Mendenhall and Elliott, it being understood that a greater number of initial or input magnetic tape tracks and a somewhat different arrangement of switches would be required in the present case.

In the foregoing manner, there can be provided stacked composite traces for 312 of the 336 reflection points shown in FIG. 2, there being six points in each comer of the array for which only a single reflection is recorded. Assuming that maximum stacking is desired, the composite traces for the reflection points R located within the area bounded by imaginary boundary line 24 are obtained by combining 16 separate reflections or folds. Similarly, the composite traces for the refelction points R located within the area between imaginary boundary lines 24 and 25 are obtained by combining 12 individual reflections or folds. The composite traces for the reflection points R in the area between imaginary boundary lines 25 and 26 are obtained by combining 8 different reflections or folds. The composite traces for the reflection points R in the area between imaginary boundary lines 26 and 27 are obtained by combining four different reflections or folds. For the remainder of the reflection points R lying outside the imaginary boundary line 27, the number of reflections which are combined are indicated by the small numerals adjacent such points as shown for the case of the reflection points in the lower left-hand corner of the FIG. 2 array.

Considering for example the reflection .point R located at X-Y coordinate point (23,24), there are 16 different source-detector pairs which produce and receive reflections from this point. The ray paths for these reflections are indicated by radial lines 28 passing through the point (23,24). For this point there is obtained one recorded reflection for each of the sources S except for the four right-hand sources located at coordinate points (48,0), (48,16), (48,32) and (48,48). Where maximum stacking is desired, the 16 individual reflection traces for the point (23,24) are individually corrected for elevation, weathering and normal moveout and the resulting corrected traces are added together to produce the single composite trace for the point (23,24).

Another important purpose which can be accomplished with an areal seismic array of the type shown in FIG. 2 is that it enables particular ones of the ray paths to be selected and displayed in a coordinated manner to provide improved indications of the subsurface geology. For example, where a fault crosses the area being surveyed, the ray paths which are interrupted by the fault provide poor data concerning the sursurface geology. On the other hand, the ray paths which run more or less parallel to the fault line and are not interrupted by same provide much better data concerning the subsurface geology. This, improved analysis can be obtained by selecting the latter type ray paths and reproducing same in a coordinated manner. The multidirectional aspect of the present embodiment makes possible such a selection of only the better data. This is accomplished by initially reproducing the various recorded reflections and studying same to obtain an approximate understanding of the perculiarities of the subsurface geology. Based upon this preliminary study, selected ones of the recorded reflections are thereafter reproduced in a coordinated manner for enabling an improved analysis of the subsurface earth structure.

In addition to selecting particular ray paths to eliminate poor data because of faults, particular ray paths can also be selected for other purposes. For example, particular ray paths may be selected to produce stacked records wherein the effect of changes in normal moveout is reduced. Also, particular ray paths may be selected having lengths of the appropriate values for minimizing undesired noise effects. Also, as a general proposition, the recorded reflections which are to be coordinated can be chosen to concentrate or focus maximum emphasis on places of particular interest.

Referring to FIG. 3, there is' shown a plan view of a seismic source and detector array as laid out on the surface of the earth in accordance with a lineal embodiment of the invention. The array of FIG. 3 includes a first set of spaced seismic detectors D located along a flrst line A and a second set of spaced seismic detectors D located along a second and different line C. Lines A and C are parallel and are spaced a substantial distance apart. The detectors D on line A are connected to a multiconductor cable which runs to a recording truck 31, while the detectors D on line C are connected to a multi-conductor cable 32 which runs to a second recording truck 33.

In practicing the method of H6. 3, seismic disturbances are produced in a sequential manner along line A at spaced source points S located at points different from the locations of the detectors D. in a similar manner, seismic disturbances are also produced in a sequentual manner along line C at spaced source points S located at points different from the locations of detectors D. Using the imaginary distance scale 35 running parallel to the detector lines for purposes of explanation, a typical procedure would be to produce a seismic disturbance at the source point (A, 0), where A denotes the detector line and the numeral denotes the distance value on the imaginary scale. The resulting subsurface reflections received by each of the various detectors D in both lines A and C are individually recorded. After this first seismic disturbance subsides, a

second siesmic disturbance is produced at source point (C, O) and the subsurface reflections thereof received by all of the seismic detectors D in both lines A and C are again individually recorded. Following this, the three seismic detectors D located at (A, 2), (A, 6) and (A, llfl) are picked up and relocated in a spaced in-line manner to the right of the right-hand end of the cable 30. Similarly, the three detectors D located at (C, 2), (C, 6) and (C, together with their interconnecting lengths of cable, are picked up and transferred to the right of the right-hand end of cable 32. Following this, a seismic disturbance is produced at source point (A, 112) and the resulting subsurface reflections received by all of the various seismic detectors D are recorded. Thereafter, a seismic disturbance is produced at source point (C, 12) and the resulting seismic reflections received by all of the detectors D are again individually recorded. Following this, the three left-hand most detectors in each of lines A and C are picked up and transferred to similar spaced positions to the right of the right-hand ends of cables 30 and 32. Seismic disturbances are then produced at the next pair of source points, the resulting reflection recorded and the next three sets of detectors in each line are picked up and transferred to the right-hand ends of the lines. In this manner, the detector lines are extended in a continuous manner until the desired length of the earths surface has been surveyed.

The foregoing method represents another application of the multi-directional technique of the present invention. More particularly, there is obtained with this method an additional line of reflection points R lying along a line B located intermediate the detector lines A and C. As is indicated by the ray paths 34 passing through the reflection point R located at (B, 21), each point along line B is sampled in a multi-directional manner. Thus, in effect a solid cone of data is obtained regarding each such reflection point R along line B, (except, of course, for the few extreme left-hand points). Thus, not only does the present method yield a greater number of reflection points but, in addition, there can be obtained for the reflection points R along line B a greater degree of stacking than can be obtained along either of the single lines A and C. In particular, twice as many reflections are obtained for each of the reflection points along line B as are obtained for the correspondong ones of the reflection points along lines A and C.

The small numerals located adjacent the reflection points in lines B and C indicate the number of reflections or folds which can be stacked, it being noted that eight different reflections can be stacked for the reflec tion point located at (B, 21), such reflections being represented by the different ray paths 34. The small numerals to the right of imaginary scale coordinate 30 are enclosed in parenthesis to show that they indicate the number of reflections obtained for the case where none of the detectors are picked up and moved from the left end to the right end of the array. Where the detectors are in fact picked up and moved in the manner previously described, there is obtained :for each of the reflection points along lines A and C to the right of imaginary scale unit 30 a total of four reflection folds and for each of the reflection points along line B to the right of imaginary scale point 30 a total of eight reflection folds, these totals remaining constant so long as the detectors continue to be picked up and transferred from left to right following each pair of seismic disturbances.

In accordance with a further feature of the present invention, both the areal method of FIG. 2 and the lineal method of FIG. 3 can be employed to provide a stacked shallow refraction survey. This is accomplished by reproducing in a coordinated manner the appropriately selected ones of the recorded reflections. The results of such refraction surveys can be used to determine the effects of refraction on the reflection survey data.

Referring now to FIG. 4, the seismic exploration system thereshown includes a relatively large number of seismic detectors D located in a two dimensional array covering a subtantial surface area of the earth. Each of the detectors D is represented by a small circle with a dot in the center thereof. More particularly, the detector array of FIG. 4 includes a first set of 12 spaced seismic detectors D located along a first line running parallel to the X axis at the zero position on the Y axis scale. These detectors D are connected to a multi-conductor cable (not shown) which runs along the X line and thence to a recording truck (not shown). The detector array further includes a second set of twelve spaced seismic detectors D located along a second and different line running parallel to the X axis and located at the Y 8 position on the Y scale. Similarly, additional sets of spaced seismic detectors D are laid out parallel to the X axis at the 16, 24, 32, 40 and 48 unit positions on the Y axis scale. These various detector lines are parallel and are spaced a substantial distance apart.

The seismic array of FIG. 4 further includes a set of four seismic sources S, each located in the vicinity of the seismic detectors D. More particularly, each of the seismic sources S is located in the immediate vicinity of a different one of the four comers of the rectangular detector array, the coordinate locations for the sources being (0, 0), (48, 0) (0, 48) and (48, 48), where the first number denotes the X axis coordinate and the second number denotes the Y axis coordinate. As is seen 'from FIG. 4, each source S is represented by a small square having a circle in the middle thereof.

The 0) sources S are activated one at a time to produce their own individual seismic disturbances during different periods of time. Assuming that the seismic source S at location (0, is activated first, then the resulting subsurface reflections received by each of the 84 seismic detectors D in FIG. 4 are individually recorded in the customary manner. This provides a comprehensive multi-point coverage of the subsurface region lying below the surface area designated as Area I in FIG. 4, this Area I quadrant being defined by coordinate points (0, 0), (0, 24), (24, 24) and (24, 0). The subsurface points from which reflections are obtained by the detectors are designated by the letter R and are represented by small black dots, a typical such dot being represented at the coordinate position (1, 0). As thus seen, there is one such subsurface reflection point R for each of the 84 detectors D in the total array. For the detector D located at (46, 48), for example, the subsurface reflection point R located at (23,24) is investigated, such reflection point being midway between the source and the detector. Similarly, the subsurface reflections from the reflection point R at (7, 16) are received by the detector D at (14, 32). Thus, it is seen that by using a two-dimensional array of seismic detectors D, there is accomplished a multi-directional exploration of Area I by the single seismic source S located at (0, 0).

After the seismic disturbance produced by the source S at (0, 0) has died out, the siesmic source S located at (48, 0) is activated to produce a second impulse type seismic disturbance. The subsurface reflections of this second disturbance are received by eadh of the 84 detectors in the total array and are individually recorded in the usual manner. This provides a comprehensive multi-point coverage of the subsurface region below Area II. In a similar manner, at subsequent points in time, the sources at (0, 48) and (48, 48) are detonated to provide comprehensive multi-point coverage of Areas III and IV, respectively.

From the foregoing, it is seen that the total area in FIG. 4 is comprehensively surveyed by the use of only four seismic source detonations. By way of comparison, if the conventional one line at a time" technique had been used, a total of 14 source detonations (two per line) would have been required for this same number of detector lines. In addition, with the present multidirectional method, approximately twice as many subsurface points are surveyed as compared to the case of the conventional in-line one line at a time method. This is seen by observing that lines of reflection points also occur at Y coordinate values of 4, l2 and 20, these lines being located intermediate the detector lines. These intermediate reflection points would not be obtained with the conventional in-line method. Thus, a greater amount of data is obtained for a given expenditure of time and labor.

It is to be understood that the specific numbers and spacings of sources and detectors shown in the foregoing embodiments are intended by way of example only. The number of sources and number of detectors, for example, can be increased or decreased for pruposes of covering a larger or smaller surface area, for purposes of increasing or decreasing the reflection point density or the like. The matter of primary importance is to arrange the sources and detectors so that reflections in difierent directions are simultaneously recorded. As indicated previously, this enables the obtaining of a greater amount of data and better quality data concerning the subsuface earth structures for a given expenditure of time and labor.

While the foregoing methods have been described with respect to their use on land, it is to be understood that such methods may also be used in water or watercovered areas such as oceans, bays, lakes, rivers, and the like.

While there have been described what are at present considered to be preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, intended to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In the art of seismic exploration by producing seismic disturbances, detecting subsurface reflections of said disturbances with seismic detectors selectively located with respect to the source points of said disturbances, and recording for analysis, study, and refinement the reflections detected by said seismic detectors, the improvement comprising:

developing multiple pieces of data from a given reflecting point by producing a plurality of seismic disturbances spaced in time from one another at source points spaced in distance from one another,

locating seismic detectors in an array to receive reflections of said disturbances from said reflecting point,

said source points and detectors being so located that a plane containing one source point, said reflecting point, and a detector is at an angle to another plane containing another source point, said reflecting point and another detector,

and recording substantially all reflections of said disturbances received by said detectors.

2. An improved seismic exploration method in accordance with claim 1 and further comprising utilizing a sufficient number of seismic disturbances and a sufficient number of seismic detectors to develop multiple pieces of data from a plurality of reflecting points in the course of a survey.

3. A method of seismic exploration in accordance with claim 2 and including:

reprocuding the recorded reflections and studying same;

and combining selected ones of the recorded reflections for producing composite records wherein plural reflections from common subsurface points are added, the selection being made to reduce the effect of changes in normal moveout.

4. A method of seismic exploration in accordance with claim 2 and including:

reproducing the recorded reflections and studying same;

and thereafter reproducing selected ones of the recorded reflections in a coordinated manner, the selected reflections being ones having ray path lengths of the appropriate value for minimizing undesired noise effects.

5. An improved seismic exploration method in accordance with claim2 in which at least some of said seismic detectors are located in said array to receive reflections from at least some of said reflecting points upon production of successive seismic disturbances without being relocated between such disturbances.

6. An improved seismic exploration method in accordance with claim 5 in which none of said seismic detectors are relocated in the course of a survey.

7. An improved seismic exploration method in accordance with claim 1 and further comprising stacking recordings representing at least some of the multiple pieces of data from said given reflecting point.

8. An improved seismic exploration method in accor dance with claim 1 and further comprising selecting for study only those recordings representing pieces of data from said given reflecting point providing better quality information concerning said reflecting point.

9. in the art of seismic exploration by producing seismic disturbances, detecting subsurface reflections of said disturbances with seismic detectors selectively located with respect to the source points of said disturbances, and recording for analysis, study, and refinement the reflections detected by said seismic detectors, the improvement comprising:

producing a plurality of said disturbances at spaced distances and times,

locating said seismic detectors in an array positioned with respect to the source points of said disturbances to receive reflections of different disturbances from at least some common reflecting points, said arrray having two dimensions in the generally horizontal plane,

and recording substantially all reflections of said disturbances detected by said seismic detectors.

10. An improved seismic exploration method in accordance with claim 9 and further comprising stacking recordings representing reflections from at least one of said common reflecting points.

11. An improved seismic exploration method in ac cordance with claim 9 and further comprising selecting for study only those recordings representing reflections from any one of said common reflecting points provid ing better quality information concerning said reflecting point.

12. A method of seismic exploration comprising:

locating a number of seismic detectors in a twodimensional array;

producing in a sequential manner seismic disturbances at a number of points in the vicinity of the seismic detectors, such points being located to pr0- duce multidirectional sampling of each of various subsurface reflection points;

and recording for each seismic disturbance the subsurface reflections thereof received by the various seismic detectors.

13. A method of seismic exploration comprising:

locating a number of seismic detectors in a twodimensional rectangular array covering a substantial surface area;

producing at different times seismic disturbances in the immediate vicinity of each of the four corners of the rectangular array;

and recording for each of the four seismic disturbances the subsurface reflections thereof received by the seismic detectors for providing a comprehensive multi-point coverage of the subsurface region below the rectangular array.

14. A method of seismic exploration comprising:

locating a first set of spaced seismic detectors along a first line;

locating a second set of spaced seismic detectors along a second and different line;

producing a first seismic disturbance at a point along 1 the first line;

producing a second seismic disturbance at a point along the second line;

and recording for each of the seismic disturbances the subsurface reflections thereof received by the seismic detectors in both the first and second sets.

15. A method of seismic exploration in accordance with claim 14 wherein the first and second lines are parallel and are spaced a substantial distance apart.

16. A method of seismic exploration comprising:

locating a first set of spaced seismic detectors along a first line;

locating a second set of spaced seismic detectors along a second and different line;

producing at different times seismic disturbances along the first line at spaced points different from the detector locations;

producing at different times seismic disturbances along the second line at spaced points different from the detector locations;

and recording for each of the seismic disturbances the subsurface reflections thereof received by the seismic detectors in both the first and second sets. 17. A method of seismic exploration in accordance with claim 16 wherein the first and second lines are parallel and are spaced a substantial distance apart.

18. A method of seismic exploration in accordance with claim 17 and including the steps of:

locating a third set of spaced seismic detectors along a third line running parallel to the first and second lines and spaced apart a substantial distance therefrom; and recording for each of the seismic disturbances the subsurface reflections thereof received by the seismic detectors in the third set. I 19. A method of seismic exploration in accordance with claim 18 wherein the third set of seismic detectors is located intermediate the first and second lines.

20. A method of seismic exploration in accordance with claim 17 and including the steps of:

locating a third set of spaced seismic detectors along a third line running parallel to the first and second lines and spaced apart a substantial distance therefrom;

producing along the third line at spaced points different from the detector locations seismic disturbances at times different from one another and from the times for the seismic disturbances along the first and second lines;

and recording for each of the seismic disturbances along each of the lines the subsurface reflections thereof received by the seismic detectors in the first, second and third sets.

21. A method of seismic exploration in accordance with claim 20 and including the steps of:

locating a fourth set of spaced seismic detectors along a. fourth line running parallel to the first and second lines and located midway therebetween;

locating a fifth set of spaced seismic detectors along a fifth line running parallel to the second and third lines and located midway therebetween;

and recording for each of the seismic disturbances the subsurface reflections thereof received by the seismic detectors in the fourth and fifth sets.

CERTIFICATE or Inventor(s) JLEE AVI Dated UNITED STATES PATENT OFFICE ,UHON

J'ULY l7, 1973 Column '4, line Column 7 line 46, change (0,)

Signed and sealed this 27th (SEAL) Attest:

EDWARD M.FLETCHER,JR. Attesting Officer It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

"refelction" to reflection-;

to Y O;

-seismic;

to Dr day of November 1973.

RENE D. TEGTMEYER Acting Commissioner of Patents 7 F OHM PO-1050 (10:69)

USCOMM-DC 60376-P69 w as GOVERNMENT PRINTING arms: was 0-355-334 i UNITED STATES PATEN'YI OFFICE CERTIFICATE OF CRECTION Patent No. 3,746,122 Dated JULY 17 1973 Inventor(s) JLEE DAVIS It is certified that error appears in the above-identified patent and that said Letters Patent are hereby correcteo} as shown below:

Column 4, line 43, change "refelction" to -reflection--;

Column 7, line 22, change "X O" to Y O-;

Column 7, line 43, change "0) to seismic;

Column 7 line 46, change (0,) to To, 0)

Signed and sealed this 27th day of November 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR RENE D. TEGTMEYER v Attesting Officer Acting Commissioner of Patents ORM PO-1050 (10-69) US COMM-DC 60376-P69 1 v1 u.s. GOVERNMENT PRINTING OFFICE: 19:9 o-aee-su 

1. In the art of seismic exploration by producing seismic disturbances, detecting subsurface reflections of said disturbances with seismic detectors selectively located with respect to the source points of said disturbances, and recording for analysis, study, and refinement the reflections detected by said seismic detectors, the improvement comprising: developing multiple pieces of data from a given reflecting point by producing a plurality of seismic disturbances spaced in time from one another at source points spaced in distance from one another, locating seismic detectors in an array to receive reflections of said disturbances from said reflecting point, said source points and detectors being so located that a plane containing one source point, said reflecting point, and a detector is at an angle to another plane containing another source point, said reflecting point and another detector, and recording substantially all reflections of said disturbances received by said detectors.
 2. An improved seismic exploration method in accordance with claim 1 and further comprising utilizing a sufficient number of seismic disturbances and a sufficient number of seismic detectors to develop multiple pieces of data from a plurality of reflecting points in the course of a survey.
 3. A method of seismic exploration in accordance with claim 2 and including: reprocuding the recorded reflections and studying same; and combining selected ones of the recorded reflections for producing composite records wherein plural reflections from common subsurface points are added, the selection being made to reduce the effect of changes in normal moveout.
 4. A method of seismic exploration in accordance with claim 2 and including: reproducing the recorded reflections and studying same; and thereafter reproducing selected ones of the recorded reflections in a coordinated manner, the selected reflections being ones having ray path lengths of the appropriate value for minimizing undesired noise effects.
 5. An improved seismic exploration method in accordance with claim 2 in which at least some of said seismic detectors are located in said array to receive reflections from at least some of said reflecting points upon production of successive seismic disturbances without being relocated between such disturbances.
 6. An improved seismic exploration method in accordance with claim 5 in which none of said seismic detectors are relocated in the course of a survey.
 7. An improved seismic exploration method in accordance with claim 1 and further comprising stacking recordings representing at least some of the multiple piecEs of data from said given reflecting point.
 8. An improved seismic exploration method in accordance with claim 1 and further comprising selecting for study only those recordings representing pieces of data from said given reflecting point providing better quality information concerning said reflecting point.
 9. In the art of seismic exploration by producing seismic disturbances, detecting subsurface reflections of said disturbances with seismic detectors selectively located with respect to the source points of said disturbances, and recording for analysis, study, and refinement the reflections detected by said seismic detectors, the improvement comprising: producing a plurality of said disturbances at spaced distances and times, locating said seismic detectors in an array positioned with respect to the source points of said disturbances to receive reflections of different disturbances from at least some common reflecting points, said arrray having two dimensions in the generally horizontal plane, and recording substantially all reflections of said disturbances detected by said seismic detectors.
 10. An improved seismic exploration method in accordance with claim 9 and further comprising stacking recordings representing reflections from at least one of said common reflecting points.
 11. An improved seismic exploration method in accordance with claim 9 and further comprising selecting for study only those recordings representing reflections from any one of said common reflecting points providing better quality information concerning said reflecting point.
 12. A method of seismic exploration comprising: locating a number of seismic detectors in a two-dimensional array; producing in a sequential manner seismic disturbances at a number of points in the vicinity of the seismic detectors, such points being located to produce multidirectional sampling of each of various subsurface reflection points; and recording for each seismic disturbance the subsurface reflections thereof received by the various seismic detectors.
 13. A method of seismic exploration comprising: locating a number of seismic detectors in a two-dimensional rectangular array covering a substantial surface area; producing at different times seismic disturbances in the immediate vicinity of each of the four corners of the rectangular array; and recording for each of the four seismic disturbances the subsurface reflections thereof received by the seismic detectors for providing a comprehensive multi-point coverage of the subsurface region below the rectangular array.
 14. A method of seismic exploration comprising: locating a first set of spaced seismic detectors along a first line; locating a second set of spaced seismic detectors along a second and different line; producing a first seismic disturbance at a point along the first line; producing a second seismic disturbance at a point along the second line; and recording for each of the seismic disturbances the subsurface reflections thereof received by the seismic detectors in both the first and second sets.
 15. A method of seismic exploration in accordance with claim 14 wherein the first and second lines are parallel and are spaced a substantial distance apart.
 16. A method of seismic exploration comprising: locating a first set of spaced seismic detectors along a first line; locating a second set of spaced seismic detectors along a second and different line; producing at different times seismic disturbances along the first line at spaced points different from the detector locations; producing at different times seismic disturbances along the second line at spaced points different from the detector locations; and recording for each of the seismic disturbances the subsurface reflections thereof received by the seismic detectors in both the first and second sets.
 17. A method of seismic exploration in accordance with claim 16 whereiN the first and second lines are parallel and are spaced a substantial distance apart.
 18. A method of seismic exploration in accordance with claim 17 and including the steps of: locating a third set of spaced seismic detectors along a third line running parallel to the first and second lines and spaced apart a substantial distance therefrom; and recording for each of the seismic disturbances the subsurface reflections thereof received by the seismic detectors in the third set.
 19. A method of seismic exploration in accordance with claim 18 wherein the third set of seismic detectors is located intermediate the first and second lines.
 20. A method of seismic exploration in accordance with claim 17 and including the steps of: locating a third set of spaced seismic detectors along a third line running parallel to the first and second lines and spaced apart a substantial distance therefrom; producing along the third line at spaced points different from the detector locations seismic disturbances at times different from one another and from the times for the seismic disturbances along the first and second lines; and recording for each of the seismic disturbances along each of the lines the subsurface reflections thereof received by the seismic detectors in the first, second and third sets.
 21. A method of seismic exploration in accordance with claim 20 and including the steps of: locating a fourth set of spaced seismic detectors along a fourth line running parallel to the first and second lines and located midway therebetween; locating a fifth set of spaced seismic detectors along a fifth line running parallel to the second and third lines and located midway therebetween; and recording for each of the seismic disturbances the subsurface reflections thereof received by the seismic detectors in the fourth and fifth sets. 